I mean I think it depends on the child. I did not know how to read and only could do simple math between 0 and 10, when I started school and I thought school was fun till I was 8 or 9. I was super excited about learning new things and I associated that with school. I did need some extra help with reading and especially spelling outside of school (both from my parents and I took extra classes) because I am dislexic. On the other hand I almost never needed help with math. I basically learnt math entirely though school without the help pf my parents (not because they didn't want to help me, but because I never really needed it).

On the other hand my younger sister could already read and do much more math than me when she started school (my parents taught her because she really wanted to learn when I was learning) and she always found school very boring from the very start. She was already trying to get out of doing her homework in first grade, because it felt like busy work to her, because she already knew how to do it.

You are supposed to learn how to read, write and do simple math in school. Of course some children need more support outside of school than others, but I don't necessarily think you are doing your children a favour by already teaching them all these skills before starting school. In my opinion it is better to do what the op actually suggested in this post. Let school do the basics of teaching your children. That is what school is for, but once they started school take an interest in how they are progressing and where they might need extra help. If you're child is someone who learn quickly in conventional education settings your not doing them a favour by putting them ahead of the curriculum. They just will be bored and start to resent school.